To all who replied:
1) Thanks for explaining how the merge feature works. I didn't realize that was how it worked. It's helpful to know.
2) Just in case it wasn't clear (and I think it was), my objection was not with regards to the merge feature, per se. It was more with regards to how it impacted message count. If the forum software is smart enough to merge my individual replies, then it should also be smart enough (IMO) to count each as an individual reply, regardless of whether or not it is merged. Perhaps that's not programmed into the vBulletin software - and there wouldn't be anything that MacRumors could do about it. Or perhaps its a preference and they could do something about it?
3) And in closing, just because the message count policy is a feature of some (perhaps even many) forums, does not make it a good policy. As I mentioned before, I think its kind of an absurd policy. Why not base the policy on tenure - or on a combination of tenure and post count? For example, for those with less than one year tenure, enforce a message count policy - for those with more than a one year tenure, enforce it differently - for those with a greater than five year tenure, enforce it differently yet again. It seems to me the purpose of such a policy is to ensure someone doesn't join the forum simply to troll the politics section. I've been a member for years - does that seem as if I joined to troll the politics forum?
Repeating my first point - I do appreciate those who took the time to explain how the merge feature works. Thanks!